First, some assumptions. I would prefer that North Korea (the DPRK) and South Korea (ROK) are reunited without war. I want to see the ROK not harmed too much economically by having to subsume a pretty dysfunctional infrastructure and economy in the North. That harm has to happen to the ROK economy to achieve reunification. There is, and will continue to be, pushback against reunification by corporate interests in the ROK, although no one will admit this.
Both militaries are itching for a fight, and both are great at what they do well. The ROK military excel technically, much like the US military. The DPRK military are possibly unmatched in unconventional warfare (think US Navy SEALS, only better, and many, many more of them), and extremely innovative in asymmetrical warfare using old platforms. It's pretty smart to crater a coastal airfield runway using BM21 rocket launchers mounted on P6 torpedo boats, a completely disposable platform, and it buys a much needed day of suppressed air support. There are other examples.
So, let's avoid all that. Were I Kim Chong Eun, leader of North Korea, one option I would consider would be to launch a very feeble invasion of South Korea, intending to lose quickly and with a minimum of loss of life. This lets Kim squander, by surrender and mis-use, the North Korean military, his only rival for power, and force the South to take a "we didn't mean to, but we broke it, so we own it" approach. Political and economic objections are thwarted, countries are reunited like East and West Germanies, rebuilding begins, problem solved. I'm sure the ROK has a plan for this contingency, the only fly in this ointment. This is a workable plan, I think.
And the problem is, North Korea doesn't seem to be thinking that way. They are developing a submarine launched ballistic missile capability. A Whiskey or Romeo-class diesel-electric North Korean Navy submarine surfacing 13 miles off the city of Los Angeles with a few hundred mile or thousand mile capable nuclear missiles sends a message. This could easily happen.
The US is floating plans for a pre-emptive strike against North Korea to take out their nukes. Unwise. Our military are completely unwilling to have any kind of ground war on the Korean peninsula, because the terrain there neutralizes our armor advantage, so there would be no follow-up. I'm pretty sure the North Koreans have not revealed the location of all their nukes to us. This plan is a fail.
But I think this is what North Korea is inviting us to do - blow up some of their stuff. How they see that resulting in a soft landing is difficult to see. It might be that Kim cannot compel his military to do the feeble invasion route, and his nuclear antics are his only way to get a big enough conflict to save the DPRK from itself.